Ophthalmic lenses are often made by cast molding, in which a monomer material is deposited in a cavity defined between optical surfaces of opposing mold parts. Multi-part molds used to fashion hydrogels into a useful article, such as an ophthalmic lens, may include for example, a first mold part with a convex portion that corresponds with a back curve of an ophthalmic lens and a second mold part with a concave portion that corresponds with a front curve of the ophthalmic lens. To prepare a lens using such mold parts, an uncured hydrogel lens formulation is placed between a plastic disposable front curve mold part and a plastic disposable back curve mold part.
The front curve mold part and the back curve mold part are typically formed via injection molding techniques wherein melted plastic is forced into highly machined steel tooling with at least one surface of optical quality.
The front curve and back curve mold parts are brought together to shape the lens according to desired lens parameters. The lens formulation was subsequently cured, for example by exposure to heat and light, thereby forming a lens. Following cure, the mold parts are separated and the lens is removed from the mold parts.
Cast molding of ophthalmic lenses has been particularly successful for high volume runs of a limited number of lens sizes and powers. However, the nature of the injection molding processes and equipment make it difficult to form custom lenses specific to a particular patient's eye or a particular application. Consequently, other techniques have been explored, such as: lathing a lens button and stereo lithography techniques. However, lathing requires a high modulus lens material is time consuming and limited in the scope of the surface available and stereo lithography has not yielded a lens suitable for human use.
In prior descriptions, methods and apparatus for forming customized lenses via the use of voxel based lithographic techniques have been described. An important aspect of these techniques is that a lens is produced in a novel manner where one of two lens surfaces is formed in a free form fashion without cast molding, lathing or other tooling. A free formed surface and base may include a free flowing fluent media included in the free formed surface. This combination results in a device sometimes referred to as a Lens Precursor. Fixing radiation and hydration treatments may typically be utilized to convert a Lens Precursor into an ophthalmic lens.
A freeform lens created in this manner may need to be measured in order to ascertain the physical parameters of the lens. Therefore, apparatus and methods are needed for measuring a lens formed from a precursor.